if so what part number is the part # for teh L69 prom I have a knock sensor and a 5 speed. Thanks

 

LG4 = Carbureted 305 CID, L69 = Carbureted 305CID (High Output)

Sounds like the difference between these two engines is the camshaft. I couldn't confirm whether you could interchange these PROMs, but even if you could, I'm not sure why you would want to do that. I'm not overly familiar with how these computer controlled carburetors worked but if we assume the ECM's purpose was to maintain proper air/fuel ratio through various driving conditions, as an ECM/PCM does with a fuel injected engine, an LG4 would not run properly with an L69 PROM because the L69 PROM is tuned for a different camshaft.

 

I have a350 now and the l69 chip is suppose to have a better timing curve.